China's sweeping overhaul of its anti-corruption architecture could enable President Xi Jinping to justify retaining his key ally and top graft buster Wang Qishan beyond retirement age, sources with ties to the leadership say.

Breaking the unwritten retirement rule could also set a precedent for Xi, 63, to defy current expectations that he will step down as party and military chief in 2022 and as state president the following year, the sources said.

A new National Supervisory Commission will combine the powers of several graft-fighting bodies, including Wang's Central Commission for Discipline Inspection (CCDI), the principal vehicle for Xi's signature anti-corruption drive.